1. Technical Field
The present invention relates to an optical component unit having an optical component housed along an inner wall of a housing component made of resin, and a laser joining method and apparatus for fixing the optical component to the inner wall.
2. Description of the Related Art
Among conventional methods for fixing optical components to a housing component made of thermoplastic resin is a method using thermal fastening in which the optical components are fixed to the housing component by provision of an interference in a mechanism for enclosing the optical components in the housing component, fixation of the housing component to a receiver jig, and deformation of the interference with heat and pressure exerted by what is called an anvil. Alternatively, there has been known a fixation method in which the optical components are bonded to the housing component with the use of ultraviolet curable adhesive.
In general, the fixation method using thermal fastening is often employed when accuracy is not so required, and the fixation method using ultraviolet curable adhesive is often employed when accuracy is required.
The optical components fixation method using thermal fastening achieves a high fixation strength and yet causes an issue in which a position accuracy for the optical components cannot be ensured. The fixation method using ultraviolet curable adhesive achieves the position accuracy and yet causes an issue in which a high fixation strength cannot be obtained. Additionally, the fixation in which the position accuracy is obtained requires ultraviolet irradiation time to be prolonged and thus causes an issue of a decrease in productivity.
Recently, a method has been proposed in which an optical component is fixed by casting a laser beam onto an inner wall of a housing component and forcing thermally melted resin between the inner wall and the optical component (Japanese Unexamined Patent Publication No. 2004-333946). It is contemplated that fixation of the optical component with high accuracy can be performed in a short tact time of several seconds in accordance with the method. Furthermore achieved are a reduction in rising time on the occasion of switching of types of machine and an improvement in productivity.
In the aforementioned fixation method with the casting of a laser beam onto the inner wall of the housing component, however, inert gas is fed solely so as to flow from the center toward the end of the optical component. Therefore, resin thermally melted into a viscous fluid state flows onto the outer periphery of the optical component, enters inside of an effective diameter of the optical component, then cools to become solid resin upon suspension of the laser radiation, and results in a decrease in the effective area of the optical component. A ratio of a length of the resin flow-in from the end face of the optical component to a radius of the optical component is larger than 0.25, and this makes it impossible to attain reduction in size and weight of the optical component unit. Besides, a portion of the resin, which is to be forced into a location between the inner wall of the housing component and the optical component for fixation of the optical component, flows onto the upper part of the optical component and thus, decreases the strength of fixation of the optical component, and there is a danger that the optical component will come off during service conditions including vibration, a fall, or the like.
On the condition that a laser beam with a spot diameter of φ 0.6 mm, 0.6 mm by 20 mm, or the like disclosed in Japanese Unexamined Patent Publication No. 2004-333946 described above is cast onto the inner wall, swelling of melted resin from the inner wall that is caused by the laser radiation exceeds 0.2 mm in a small-size optical component unit of which a height from a top of a wall surface of the optical component to a top of the inner wall of the housing component is not larger than 1 mm. This is because the laser beam having the width of 0.6 mm causes melting of the resin to extend to surroundings of the width by reason of heat conduction and causes an upper surface of the inner wall to be melted and solidified. Though a decrease in the power of the radiation may prevent the swelling from occurring, a decrease in the amount of the resin that is forced between the inner wall and the optical component for fixation of the optical component results in failure of the fixation or extremely low fixation strength. Products using optical component units in recent years have a notable inclination toward a decrease in size and thickness, and optical component units having a height of the inner wall lower than 1 mm and having no swelling are desired. Thus, the occurrence of the swelling on the upper surface of the inner wall prevents the desired decrease in size and thickness of the product.
Use of such a laser may melt a receiving surface that holds the optical component. When the laser beam is cast onto a portion of the optical component in the vicinity of the inner wall, a traveling direction of the laser beam changes because of a difference in refractive index, so that the laser beam is cast onto the receiving surface that holds the optical component. In this situation, the receiving surface is melted and swells up, and an interval is changed between surfaces of the optical component and another optical component, and thus performance as the optical component unit is deteriorated.
It is an object of the present invention to provide an optical component unit, and a laser joining method and apparatus for optical component each of which allows an effective diameter of an optical component to be increased with a ratio of a length of resin flow-in to a radius of the optical component being not larger than 0.25, which can be decreased in size and thickness by prevention of swelling of an inner wall, and in which evenness on a receiving surface of a housing component prevents deterioration in the performance of the optical component.